software-defined iot: 6tisch centralized scheduling and multipath construction

1

6TiSCH Centralized Scheduling and Multipath Construction

Hao Jiang

Industrial Mentor: Pascal Thubert

September 21st, 2016

Academic Coordinator: Géraldine Texier

1

2

• The art: 6TiSCH multipath forwarding with BIER-TE (5 min)

• Internship: 6TiSCH multipath control with BIER-TE (8 min) + Demo (3 min)

• Testbed Implementation (2 min)

• Multipath Control Loop Experiments (8 min) + Demo (3 min)

• Conclusion (1 min)

• Q&A

Agenda

2

3

Mission: optimize delivery within time and energy constraints

Bring deterministic properties to Low-power and Lossy Networks (LLNs)

based on 6TiSCH (IPv6 over the TSCH mode of IEEE 802.15.4e):

• Scheduling over Time Slotted Channel Hopping (TSCH)

• Packet replication and elimination over redundant routes with BIER-TE

Figure 2: 6TiSCH Protocol Stack (a) and

Architecture (b)

0 1 2 3 4 5 6 7 8

0

1

2

3

4 A->B

5

6

7 B->C

8

9

10

11

12 A->C

13

14

15

A

B

C

slot

Offset1 2

channel

Offset4 12

Neighbor B C

Type TX TX

slot

Offset1 5

channel

Offset4 7

Neighbor A C

Type RX TX

slot

Offset2 5

channel

Offset12 7

Neighbor A B

Type RX RX

L B T TX FRAME RX

ACKRX FRAME

TX

ACK

Network topologyTSCH Schedule

Node A schedule Node B schedule

Node C schedule

Transmitting time slot

(LBT : Listen Before Talk)Receiving time slot

time

fre

qu

en

cy

D

C->B

B->D

C->D

6

2

C

RX

7

10

D

TX

6

2

B

TX

slot

Offset

channel

Offset

Neighbor

Type

Node D schedule

7

10

B

RX

8

5

D

TX

8

5

C

RX

Figure 1: TSCH Schedule

(a)

(b)

3

4

The art: 6TiSCH multipath forwarding with BIER-TE

Packet replication and elimination is controlled by BIER-TE (Bit-Indexed Explicit Forwarding – Traffic Engineering):

• Every packet contains a bitString in header with each bit representing an adjacency;

• If a bit of an adjacency is SET to ‘1’ in the bitString, a node would RESET the bit to ‘0’ and send a copy to the adjacency;

• If received multiple copies, a node performs an AND operation on the bitStrings and keeps only one copy.

Figure 1: BIER-TE Multipath Forwarding with Full Replication4

5

BIER-TE Multipath Forwarding Rules

Let’s assume A has a packet with a bitString ‘11111111’, and the link from B to D is broken.

0 1 2 3 4 5 6 7 8 9

A->B A->C B->C C->B B->D C->E D->E E->D D->F E->F

B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

Bit Neighbor

0 B

1 C

A’s BIFT

Schedule:

5

6

Slot 0: A resets bit 0 and sends a copy of the packet to B

0 1 2 3 4 5 6 7 8 9


01111111

B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

Bit Neighbor

0 B

1 C

A’s BIFT

Schedule:

6

7

01111111

Slot 1: A resets bit 1 and sends another copy to C

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

10111111

Bit Neighbor

0 B

1 C

A’s BIFT

Schedule:

7

8

10111111

01011111

01111111

Slot 2: B resets bit 2 and sends a copy to C

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

Bit Neighbor

2 C

3 D

B’s BIFT

Schedule:

8

9

00011111

01111111

Slot 2: C performs an AND operation on the bitStrings and drops a copy

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

10111111

01011111

Schedule:

9

10

00011111

01111111

Slot 3: C does not send a copy to B, as bit 2 is not SET

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

Bit Neighbor

2 B

4 E

C’s BIFT

Schedule:

10

11

00011111

01111111

Slot 4: Transmission fails, and D does not get the message

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

Bit Neighbor

2 C

3 D

B’s BIFT

Schedule:

11

12

00011111

01111111

Slot 5: C resets bit 4 and sends a copy to E

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

00010111

Bit Neighbor

2 B

4 E

C’s BIFT

Schedule:

12

13

00011111

01111111

Slot 6: D has nothing to send

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

00010111

Bit Neighbor

5 E

6 F

D’s BIFT

Schedule:

13

14

00011111

01111111

Slot 7: E resets bit 5 and sends a copy to D

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

00010111

00010011Bit Neighbor

5 D

7 F

E’s BIFT

Schedule:

14

15

00011111

01111111

Slot 8: D resets bit 6 and sends a copy to F

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

00010111

00010011

00010001

Bit Neighbor

5 E

6 F

D’s BIFT

Schedule:

15

16

00011111

01111111

Slot 9: E resets bit 7 and sends a copy to F

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

00010111

00010011

00010001

00010110

Bit Neighbor

5 D

7 F

E’s BIFT

Schedule:

16

17

00011111

01111111

Slot 9: F performs an AND operation and forwards a copy to upper layer

0 1 2 3 4 5 6 7 8 9


B

A

C

D

0

2

6

E

F

1

4

3

5

7

11111111

00010111

00010011

00010000

00010001

00010110

The output bitString can be passed to

the controller to identify transmission

failures and deduce link conditions, in

return, the controller can accordingly

modify the bitString for next packets.Schedule:

17

18

Internship: 6TiSCH centralized scheduling and multipath construction with BIER-TE

Figure 2: 6TiSCH Centralized Architecture

Goal

explore centralized operations with a PCE on control plane to improve the delivery ratio while lowering energy budget

Content

Topology Discovery, Multipath Computation, Resource/Track Reservation, BitString-based Multipath Dynamic Control

18

Figure 1: BIER-TE Multipath Control

19

Topology Learning Track Computation Track Reservation Multipath Control

RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks) Non-storing mode defines:

each node periodically unicast a list of its parents to the DAG root, which normally directly connects to the controller.

Data plane work

• Multipath Selection Algorithm based on the DAG rank

• RPL DAO message compression

Control plane work

• Topology Monitoring

Figure 1: Multi-parent Selection and Advertisement

A’s neighbor list:

19

20

Implementation on OpenWSN open-source code

• Each mote selects a maximum of 5 parents with different preferences;

• A compressed DAO can contain 5 parents’ and 1 child’s information;

• The controller updates topology information each time receiving a DAO.

Figure 1: an example network in simulation

Figure 3: a compressed DAO dissected by revised

Wireshark dissector

Figure 2: received DAO messages from the nodes Figure 4: Controller’s view of topology learned from RPL


20

21

Based on the topology exposed by RPL, a variation of ARCs (Available Routing Constructs) algorithm is used to compute

the track, with a general shape of a ladder from the source to the destination.

ARC Basics

An ARC is a loop-free ordered set of nodes and links whereby the data traffic may

enter via any node of it but may only leave it through either one of its edges.

Each ARC is composed of 3 subsets {Left Exit}{Intermediate Nodes}{Right Exit}.

The links between intermediate nodes are made reversible (except for the last ARC).

Goal

The idea is to protect each hop of a path with an ARC starting from the destination.

As a result, each node would have 2 alternative outgoing links to reach the destination.

A

BC

DE

FG

H

I

Figure 1: an example track from H to A


21

22

After computing the track, the controller:

• signals each node along the track to reserve time slots for each transmission;

• assigns each segment an associated bitPosition/bitIndex in the bitString;

• installs the BIFT (Bit-Indexed Forwarding Table) on each node;

• assigns a dedicated bitString to the ingress node of this track.

16

ch

an

ne

l o

ffse

ts

e.g. 24 time slots (240ms)

Figure 1: reserved time slots for the track

A

BC

DE

FG

H

I

Figure 2: the computed track from H to A

1

0

7

3

4 5

6

8

2

9

1110


22

23

Implementation

• a reversible link means two timeslots for both directions

• first transmission first timeslot

• the bits of a bitString should be enabled according to

policies and link conditions

Figure 2: the computed track based on the topology

Figure 1: topology learned from RPL

Figure 3: reserved slots for the track

node type frameID action cell information

A schedule 1 add {‘type’: ‘tx’, ‘slotOffset’: 1, ‘channelOffset’: 4, ‘shared’:

False, ‘trackID’: 1, ‘bitIndex’: 0, ‘BIER’: True}

B schedule 1 add {‘type’: ‘rx’, ‘slotOffset’: 1, ‘channelOffset’: 4, ‘shared’:

False, ‘trackID’: 1, ‘bitIndex’: 0, ‘BIER’: True}

Table 1: example signaling data structure for the reservation of transmission from A to B

Topology Learning Track Computation and Reservation Multipath Control

23

24

Topology Learning Track Computation and Reservation Multipath Control

24

25

Goal

Enable multipath/packet replication mechanism only when necessary to save energy while maintaining high reliability.

Steps

• Set up a real hardware testbed;

• Validate experimentally the value of path diversity;

• Analyze when and how the mechanism should be activated;

• Based on the conclusions, design and implement a bitString feedback control loop.

Topology Learning Track Computation and Reservation Multipath Control1

6 c

ha

nn

el o

ffse

ts

e.g. 24 time slots (240ms)

Figure 1: enabled timeslots for single path

001001010010

A

BC

DE

FG

H

I

Figure 2: enable single path when link quality is good

1

0

7

3

4 5

6

8

2

9

1110

25

26

Testbed Implementation Multipath Experiments Dynamic Multipath Control

Figure 2: a Rover node Figure 3: a local view of the testbed

Figure 1: the testbed architecture

• Raspberry Pi 3

• OpenWSN open-source code

• OpenMote hardware

Submitted paper :

Rover: Poor (but Elegant) Man’s Testbed.

Zacharie Brodard, Hao Jiang, Tengfei Chang, Thomas Watteyne,

Xavier Vilajosana, Pascal Thubert, Geraldine Texier.

ACM International Symposium on Performance Evaluation of Wireless Ad Hoc,

Sensor, and Ubiquitous Networks (PE-WASUN), Valletta, Malta, 13-17 November 2016.

26

27


Figure 1: Deployment at Cisco PIRL (Paris ILM Office: 6th Floor) 27

28


with retries with retries

Figure 1: experiment tracks with different scheduling patterns

28

29

• Loss

• Burstness

• Jitter

• Delay

• Energy

• Reliability


29

30

Conclusion

Multipath improves delivery by providing additional reliability with spatial diversity.

• Multipath reduces burst losses;

• Multipath overcomes node or link failures;

• Multipath introduces no jitter and bounded latency by design;

• Parallel concurrent multipath increases reliability without introducing additional delay;

• Packet replication and elimination introduces delay and more energy consumption.

Retries provide more efficient packet delivery with some limitations.

• Retries are highly valuable only with channel hopping;

• Stochastic retries introduce delay and jitter;

• Retries are less immune to burst losses: if a transmission failed, using retries has greater chance to fail again.


30

31

a single path with retries is used for efficient packet delivery and less power consumption, and the multipath mechanism

is enabled only when necessary to provide higher reliability and eliminate burst losses.

BitString Control Loop


B

A

C

D

0

2

6

E

F

1

4

3

5

7

01001001

00000000

Controller

31

32





B

A

C

D

0

2

6

E

F

1

4

3

5

7

01001001

ControllerLoss +1

32

33





B

A

C

D

0

2

6

E

F

1

4

3

5

7

01001001

Controller

33

34





B

A

C

D

0

2

6

E

F

1

4

3

5

7

Controller

11111111

Loss +1

34

35





B

A

C

D

0

2

6

E

F

1

4

3

5

7

Controller

11111111

Loss +100001000

35

36





B

A

C

D

0

2

6

E

F

1

4

3

5

7

Controller

10010010

Loss +1

36

37





B

A

C

D

0

2

6

E

F

1

4

3

5

7

01001001

Controller

00000000

37

38


38

39

Control loop experiments during nighttime

Figure 1: Receiving delays (in Time Slots)

frequency (% of messages sent)

Figure 2: Burst losses with different lengths (in the number of packets)

occurrence among 16141 messages sent

Packet Loss

39

40


Figure 1: Number of enabled bits over time in an hour

Energy Consumption

40

41


41

42

Figure 1: Receiving delays (in Time Slots)

frequency (% of messages sent)

Control loop experiments during daytime

Figure 2: Burst losses with different lengths (in the number of packets)

occurrence among 4797 messages sent

Packet Loss

42

43


Figure 1: Number of enabled bits over time

Energy Consumption

43

44


Upper path Lower path

Dynamic multipath Full replication

44

45

Summary

• Centralized operations: Topology learning from RPL, Track computation and reservation based on ARC, etc.

• Testbed setup: OpenWSN open-source code, OpenMote hardware, Raspberry Pi 3

• Multipath experiments: TSCH retries vs. multipath

• Control loop

Constraints

• Static in-building testbed topology

• Limited number and pattern of experiments

• ARC construction order issue (to be solved)

• Control loop schedule is not optimized

• Hardly reproducible

Future Work

• Dynamic scheduling

Conclusion

45

Figure 1: BIER-TE Multipath Control

46

Accomplishments

[1] P. Thubert, Z. Brodard, H. Jiang, G. Texier. IETF Draft. “A 6loRH for BitStrings”. Current version: draft-thubert-6lo-bier-dispatch-01. Available

online: https://tools.ietf.org/html/draft-thubert-6lo-bier-dispatch-01. June 29, 2016.

[2] P. Thubert, Z. Brodard, H. Jiang. “TIMESLOT SHIFTING FOR LOWER-PRIORITY PACKET IN A TIME SLOTTED NETWORK”. Filed

12-Jul-2016. U.S. Patent.

[3] Z. Brodard, H. Jiang, T.F. Chang, T. Watteyne, X. Vilajosana, P. Thubert, Géraldine Texier. “Rover: Poor (but Elegant) Man's Testbed”. 13th

ACM PE-WASUN 2016. Submitted September 04, 2016.

[4] P. Thubert, Z. Brodard, H. Jiang, T. Watteyne, T.F. Chang, T. Matsui, G. Z. Papadopoulos, G. Texier, N. Montavont. “Leapfrog Collaboration”.

Work in Progress.

[5] Z. Brodard, P. Thubert, H. Jiang, T. Watteyne, T.F. Chang, G. Texier, G. Z. Papadopoulos, N. Montavont. “Multipath Redundancy for Wireless

Time-Slotted Networks”. Work in Progress.

[6] P. Thubert, Z. Brodard, H. Jiang. “BIER-TE-based OAM, Replication and Elimination”. Current version: draft-thubert-bier-replication-

elimination-00. Available online: https://tools.ietf.org/html/draft-thubert-bier-replication-elimination-00. September 14, 2016.

46

https://tools.ietf.org/html/draft-thubert-6lo-bier-dispatch-01

https://tools.ietf.org/html/draft-thubert-bier-replication-elimination-00

47

Source code directories

47

Thank you.

49

The 6LoRH for BitStrings

50

BIER-TE Forwarding Rules

51

6TiSCH BIER-TE Data Structures

52

Multipath Experiments Configurations

with retries with retries

BIER-TE Track Description

B->C

C->B

B->D

C->D

Multipath with full replication Packets are replicated at every step (replication points) of the ladder

Low latency multipath without

retries

Use snooping and concurrent transmissions to minimize the latency

Low latency multipath with

retries

Provide a retry for each hop of the low latency multipath

Table 1: BIER-TE Track Description

Table 2: Slot AllocationTable 3: Experiment Parameters

53

New Architecture of OpenVisualizer

54

Rover Architecture

55

Track Reservation Interaction Diagram

56

Internet-to-BIER Message Handling Interaction Diagram

57

Deepening: Fast Resynchronization on Channel Hopping Mode

58

Backup Path Setup Demo

59

Backup Control Loop Demo